A-LevelBiologyControl and coordination9700/42 · Feb/Mar 2018 · Q512 Marks

The contraction of striated muscle is explained by the sliding filament model.

(a)(i)Describe what happens in the sarcomere when the myosin head releases ADP and inorganic phosphate (Pi).[1]
(a)(ii)Explain the precise function of ATP in the sliding filament model.[3]
(b)(i)Ultrafiltration requires a high blood pressure in the glomerulus. Explain how this high blood pressure is achieved.[1]
(b)(ii)Name the main filtration barrier in the nephron that allows creatinine to pass into the renal capsule but stops red blood cells from passing through.[1]
(c)(i)Describe the relationship shown in Fig. 5.2.[2]
(c)(ii)Use Fig. 5.2 to estimate the concentration of creatinine in the blood that indicates a normal GFR. answer[2]
(c)(iii)Suggest two reasons why the GFR could decrease.[2]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2018). The mark or mark type is shown in brackets.

[1] sarcomere shortens / Z lines move closer together or ref. to rowing motion of the head / power stroke ;
[3] any three from:
1 (ATP) binds to myosin head;
2 hydrolysed by, ATPase / myosin head;
3 head detaches from actin;
4 head tilts back to original position;
[1] afferent arteriole is wider than efferent arteriole;
[1] basement membrane ;
[2] any two from:
1 the higher the creatinine concentration the lower the GFR ; ora A inversely proportional
2 exponential curve / non-linear ; A description of non-linear
3 data quote for two points including units ;
[2] 0.013; g dm⁻³;
[2] any two from:
1 kidney, disease / damage ;
2 cancer;
3 dehydration;
4 low blood pressure; A loss of blood

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